Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-05-23
2004-08-10
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S046012, C372S049010, C438S039000, C438S041000
Reexamination Certificate
active
06775310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device which has a double hetero structure portion in which an active layer is sandwiched by semiconductor layers having a larger band gap than that of the active layer such that a light emitting layer is formed, such as a light emitting diode (LED), a laser diode (LD) having stripe groove and a vertical cavity surface emitting laser (VCSEL) which emits laser light from a surface of the laminated semiconductor layers, and a manufacturing method thereof. In particular, the present invention relates to a semiconductor light emitting device in which a radiating efficiency from side wall portions of the double hetero structure portion can be improved, light leakage can be reduced so as to enable efficient light emission in a narrow area and an efficiency of light outputted with respect to light inputted can be improved, and a manufacturing method thereof.
BACKGROUND OF THE INVENTION
A conventional surface emitting type semiconductor laser manufactured by a simple process has a structure shown by cross-sectional explanatory views in
FIGS. 5A and 5B
. In
FIGS. 5A and 5B
, a lower multi-layer reflection film
62
which is formed of a laminated structure referred to as DBR (Distributed Brag Reflector) is formaed on a semiconductor substrate
61
formed of, e.g., GaAs. On the lower multi-layer reflection film
62
, a lower spacer layer
63
, an active layer
64
and an upper spacer layer
65
are successively grown. On the upper spacer layer
65
, an upper multi-layer reflection film
67
formed of DBR is formed. Then, as shown in
FIG. 5A
, an insulating area
68
is provided on an outer periphery side of a current injection area by implanting ions such as protons. Alternatively, the outer periphery side may be removed by etching as shown in FIG.
5
B. Unillustrated upper and lower electrodes are respectively provided on the surface of the upper multi-layer reflection film
67
and on a rear surface of the semiconductor substrate
61
such that laser beam light can exit from a part of the upper surface.
In accordance with the above-described structure, current is injected into a narrow area serving as the current injection area, and then light with high intensity is emitted. Further, the upper and the lower multi-layer reflection films
62
and
67
resonate as a reflecting surface of cavity resonator. Thus, laser resonance occurs and a part of resonated light exits as laser beam light from a small exit opening (not shown) formed at the upper electrode through the upper multi-layer reflection film
67
which is formed so as to have a smaller reflectance than the lower multi-layer reflection film
62
.
As described above, in a conventional surface emitting type semiconductor laser, optical confinement in a vertical direction is accomplished by the upper and the lower multi-layer reflection films and light emission in a horizontal direction does not occur by insulation or removal such that efficient light emission can be accomplished by injecting the current only in the light emitting area. However, since the current centralizes only in the narrow central portion and only the area emits light, an increase in temperature in the area is significant. In the structure shown in
FIG. 5A
, as the semiconductor layer serving as an insulating area is formed on the periphery of the light emitting area, heat capacity is relatively large. However, the semiconductor layer used for a light emitting device does not have so large heat conductivity and heat generated in the light emitting area cannot be sufficiently diffused. Thus, the semiconductor layer is easily deteriorated and a luminous efficiency is also easily decreased. Especially in the structure that the periphery of the current injection area is removed by etching as shown in
FIG. 5B
, heat generated at a time of light emitting cannot be diffused efficiently. For this reason, there arise problems in that the luminous efficiency is decreased and the semiconductor layer is partially damaged such that a lifetime of the laser is reduced.
The current is centralized on the narrow area to carry out efficient emission. However, in the surrounding non light emitting area, the semiconductor layer has the same composition as that of the light emitting area into which the current is injected. The non light emitting area is formed so as to have larger electric resistance due to crystal defects being generated by ion implantation. The light emitted at the current injection area easily travels toward the insulting area, so that light cannot be confined only in the current injection area. For the light which has traveled into the insulating area, according to a difference of refractive index between the insulating area and an air layer, around 30% of reflectance can be obtained at a side surface of the insulating area. At the same time, however, an amount of light leaked is significantly large. In this problem about optical confinement, even the structure shown in
FIG. 5B
that the outer periphery of the current injection area is removed by etching has an effect of optical confinement of around 30% with respect to total reflection on a basis of a difference of refractive index derived from direct contact with air. Accordingly, there arise problems in that a resonance efficiency cannot be sufficiently increased and thus a threshold is increased.
Such problems are not limited to the surface emitting type semiconductor laser. An LED and an LD having stripe groove have problems in that light leaks from a chip side surface of the LED or the LD (from a side surface which is perpendicular to a laser light exiting surface in a case of LD) and thus is wasted.
SUMMARY OF THE INVENTION
The present invention was devised in order to solve the above-described problems, and an object of the present invention is to provide a semiconductor light emitting device that radiating characteristic of the periphery of a light emitting area of the semiconductor light emitting device which emits light by injecting current into a part of area can be improved, an optical confinement efficiency of the periphery of the light emitting area can be improved, and thus an efficiency of light outputted with respect to a certain input can be improved, a reliability can be improved by reducing damages of semiconductor layer, and a manufacturing method thereof.
Another object of the present invention is to provide a structure for enabling improvement of heat diffusion of surface emitting type semiconductor laser in which a vertical cavity is formed by making an area of double hetero structure portion into which current is injected smaller than an area of substrate and for enabling improvement of an efficiency of light outputted, and a manufacturing method of the surface emitting type semiconductor laser.
In accordance with the present invention, a semiconductor light emitting device includes: a semiconductor substrate; and a double hetero structure portion formed on the semiconductor substrate and in which an active layer having small band gap is sandwiched between semiconductor layers having larger band gap than that of the active layer, wherein a heat radiating film which has light reflecting property and superior heat conductivity than that of the double hetero structure portion is formed at least a part of side walls of the double hetero structure portion. The side wall refers to as a surface which extends in a direction vertical to a surface of the semiconductor layers are laminated. In a case of the semiconductor element, the semiconductor layers may be laminated so as to obtain an LED, a stripe type LD or a surface emitting LD.
Because of this structure, light which is emitted from the active layer and travels toward the side walls is not emitted from the side walls and confined within the light emitting area. Further, the light contributes to oscillation within a resonator in a case of the semiconductor laser, or to emit light in a predetermined direction in a case of the LED. In both of the case
Ichihara Jun
Sai Hironobu
Ip Paul
Menefee James
Rabin & Berdo P.C.
Rohm & Co., Ltd.
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